(a) Field of the Invention
The present invention relates to a converter. More particularly, the present invention relates to a quasi-resonant converter.
(b) Description of the Related Art
A converter transforms one DC voltage to at least one other DC voltage. The DC output voltage outputted from the converter can be greater or smaller than an input voltage. Such a converter is usually used in power electronic devices, particularly, battery power supplies such as a mobile phone or a laptop computer.
Quasi-resonant converters are widely used at present because a quasi-resonant converter increases power conversion efficiency and reduces electromagnetic interference (EMI). Generally, a quasi-resonant converter turns on a switching transistor when the lowest voltage is applied to both ends of the switching transistor due to a resonance. By such a scheme, a switching noise and a switching loss can be reduced in the quasi-resonant converter.
When an output load decreases in the quasi-resonant converter, a switching frequency increases, because the peak of the current flowing through a switching element decreases. When the switching frequency increases, the switching loss increases too.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.